Arc-breaking and quenching unit for electric circuit breakers

ABSTRACT

An arc-quenching system of the magnetic blast type for electric circuit breakers wherein a pair of cooperating circuit breaker contacts are disposed in an arc-quenching chamber and are juxtaposed with respective arc-splitting primary electrodes located on opposite sides of the chamber and a pair of arc displacement secondary electrodes spaced apart above the primary electrodes such that, upon opening of the circuit breaker contacts, the circuit breaking arc is generated initially between the open contacts and thereafter jumps between the contacts and the primary electrodes and a proximal secondary electrode as well as between the secondary electrodes to form an arc path consisting of a substantially regular hexagon at approximately 0.01 second subsequent to contact opening. The secondary electrodes are in series with a blast coil having magnetic poles flanking the secondary electrodes and inducing the arc to move upwardly through a quenching column formed with packs or stacks of ceramic plates adapted to increase the arc length. The cooperating juxtaposed contact surfaces of the circuit breaker contacts being substantially parallel immediately upon opening and lying in planes generally perpendicular to the arc path therebetween.

United States Patent [72] Inventor Enrico Baldlnl Primary Examiner-Robert S. Macon Berglmo, Italy Artorney-Karl F. Ross [21] Appl. No.17,621 [22] Filed Mar. 9, 1970 [45] Patented De 7, 1971 ABSTRACT: Anarc-quenching system of the magnetic blast [73] AssigneeMagrinLFabbriche Rlunlte Mlgrlnl Scarpn type for electric circuitbreakers wherein a pair of cooperating e Magnm -M,S M,.S ,A, circuitbreaker contacts are disposed in an arc-quenching Milan, lul chamber andare juxtaposed with respective arc-splitting pri- [32] Priority Mar. 10,I969 mary electrodes located onopposite sides of the chamber and [33] [ma pair of arc displacement secondary electrodes spaced apart [31] 13872A/69 above the primary electrodes such that, upon opening of the circuitbreaker contacts, the circuit breaking arc is generated initiallybetween the open contacts and thereafter jumps [54] ARC-BREAKING ANDQUENCI-IING UNIT FOR between the contacts and the primary electrodes anda prox- ELECTRIC CIRCUIT BREAKERS imal secondary electrode as well asbetween the secondary 6Clalrns,5 Drawing Figs. electrodes to form an arcpath consisting of a substantially [52] US. Cl 200/147 R regular hexagonat approximately second subsequent to [51 1 Int Cl "01h 33/18 contactopening. The secondary electrodes are in series with a [50] Field 0sarch h 200/147 blast coil having magnetic poles flanking the secondaryelectrodes and inducing the arc to move upwardly through a [56] Ru (m dquenching column formed with packs or stacks of ceramic UNITED STATESPATENTS plates adapted to increase the arc length. The cooperatingjuxtaposed contact surfaces of the circuit breaker contacts being 322:2:substantially parallel immediately upon opening and lying in 3,307,0042/1967 Bottonari 200/147 x Pm-ss-gfigmuy pmendcular the arc paththerebetween r9 0.,- 1m- 1 t g l I i fo 44-15 Hit {m 6 HI ,lilb I m 5 l"H I I t y 41 slim 1 48 40 i iiiq 7c Sci iwl i m 41 :-2 2*" z j ui--- Ir 3* a e A 'x e I 8 7: 2

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PATENTED nu: Hen W 1 OF 4 3.626.127

F l G. 4

Enrico Baldini INVIJN'I'OR.

A g'quss Attorney Fiel E nrI'CO Ba/dim' INVEN'IUR.

Attorney PATENTED DEC 7 I97! SHEET [1F 4 FIG. 5

Pie. 4

Enrico Baldini INVISN'IY'UR.

ARC-BREAKING AND QUENCIIING UNIT FOR ELECTRIC CIRCUIT BREAKERS FIELD OFTHE INVENTION My present invention relates to arc-quenching arrangementsfor electric circuit breakers and the like and, more particularly, to anarc-quenching system of the magnetic blast type in which are quenchingis carried out by subdividing the circuit breaking arc into a pluralityof secondary arcs and magnetically inducing arc movement through anarcquenching column.

BACKGROUND OF THE INVENTION Electric circuit breakers have been providedheretofore with arc'quenching arrangements operating under the principlethat high-voltage circuit breaking electric arcs, struck between therelatively movable contacts of a circuit breaker upon opening can bequenched by splitting the primary are between the contacts into two ormore secondary arcs with the aid of electrodes to which the arc istransferred, whereupon the secondary arcs are displaced through aquenching column, generally containing heat-resistant, nonconductivemembers adapted to increase the arc length, curl the arc sections andthereby extinguish the arc.

Several principles are involved in arc quenching of this nature.Firstly, the arc struck between the contacts of the circuit breaker isproduced when the gas (generally air) or other dielectric in the gapbetween the contacts is ionized. In gasopening circuit breakers in whichgas is ionized in the manner described, quenching is carried out atleast in part by thermally induced movement of the ionized gasessustaining the arc-type discharge away from the contacts, therebyincreasing the arc length until the discharge can no longer besustained. In such blast-type arc-quenching arrangements for circuitbreakers, the efficiency may be increased by promoting the movement ofthe gas through the quenching chamber.

In conjunction with arc-quenching systems of this character, it has beenproposed to subdivide the circuit breaking are at least in part bytransferring the primary arc to secondary or auxiliary electrodes spacedapart in the arc-quenching chamber. Two electrodes in spaced-apartrelationship may thus be provided in the arc-quenching chamberindependently of the contacts and in such orientation that the primaryarc struck between the circuit-opening contacts will be transferred tothese electrodes shortly after the contacts have opened to some extent.Secondary arcs are then formed between each contact and one of theseelectrodes as well as between the electrodes. By thereby increasing thearc length, the blast effect and quenching is promoted.

The arc itself is an electric current having the properties of electriccurrent flow through a conductor and thus is associated with a magneticfield. Especially when the arc is formed into a loop or curl, as isinvariably the case when the dielectric movement displaces the centralportions of the arc upwardly, the magnetic field accompanying thecurrent flow reacts to drive the arc further away from the contacts andthus additionally promotes arc quenching.

It has already been proposed, using the latter principles, to providemagnetic blast arc quenching by disposing an electromagnetic system inthe arc-quenching chamber. The poles of the electromagnetic arrangementinduce a magnetic field which cooperates with the magnetic fieldassociated with the arc itself to augment the movement of the arethrough the quenching chamber and thereby further promote extinction.The electrodes may be separated by, and the chamber provided with,stacks of arc-breaking plates which remain undamaged by the are but havethe task of increasing the arc path length between the electrodes orbetween each contact and the respective electrode such that, incooperation with the tendency of the magnetic field and the gas movementto displace the arc, an early quenching is assured even with quenchingchambers of relatively limited size.

The principles involved in the use of arc-lengthening plates have beendescribed in commonly assigned copending applications, Ser. No. 630,592filed Apr. 13, 1967 (now U.S Pat. 3,518,387) and Ser. No. 635,346 filedMay, 2, 1967 (now abandoned).

The present invention is particularly applicable to arequenching systemsof the magnetic blast type, i.e., to systems as described above in whichmagnetic poles are provided and are energized by blast coils which maybe connected with the electrodes so as to generate the magnetic fieldupon transfer of the arc to these electrodes.

Prior art systems of this character are generally of complexconstruction, are provided with parts prone to failure and requiringreplacement and are of relatively large size. They are, moreover,sensitive to the construction of the ceramic plates and the positioningthereof and, in addition to their large volume, are heavy and oftenprohibitively expensive to construct and maintain. They are alsocharacterized by relatively low arc-quenching efficiency as measured,e.g., in terms of the time required for total arc extinction.

OBJECTS OF THE INVENTION It is, therefore, the principal object of thepresent invention to provide an improved arc-quenching system of themagnetic blast type in which the speed of arc quenching and thearcquenching efficiency is increased.

it is another object of the invention to provide an improved circuitbreaker and arc-quenching arrangement which is of relatively low costand small size, but which affords more effective and rapid quenchingthan earlier systems of the same general type.

SUMMARY OF THE INVENTION These objects and others which will becomeapparent hereinafter are attained, in accordance with the presentinvention, in a circuit breaker arrangement in which two electrodes ofupwardly divergent configuration are disposed in the arcquenchingchamber in spaced relationship with the cooperating circuit breakercontacts, the primary electrodes or arc horns being proximal to therespective contacts at least upon opening of the contacts and beingseparated by a stack of refractory nonconductive plates defininggenerally a zigzag arc path between them.

Spaced above the circuit breaker contacts and the divergent portions ofthese primary electrodes or are horns, is at least one pair ofspaced-apart arc displacement horns or secondary electrodes to which thearc is transferred from the primary electrodes as the arc is induced torise upwardly in the quenching chamber, the secondary electrodes beingspaced apart by a further stack of plates.

1 have found, most surprisingly, that the efficiency of an arcquenchingsystem as described can be improved remarkably by constituting thearcing or circuit breaker contacts with mutually juxtaposed andcooperating stretches or surfaces which are substantially flat andparallel to one another at least upon incipient openings so as toestablish two closely spaced current paths adapted to induce themagnetic field which tends to push the arc upwardly and toward thearcing horns or primary electrodes. To this end, the contacts areprovided in their mutually juxtaposed regions as relatively flat memberslying substantially in a common plane and as upstanding formationshaving at upper parts thereof the actual mutually engaging contactswhile being connected at lower parts, i.e., below these flat portions,with the respective terminals of the circuit breaker.

It is, therefore, an essential feature of the present invention that thearcing contact surfaces below the faces between which the arc strikesare mutually juxtaposed and face one another in both the closed positionof the contacts and on incipient opening; these surfaces are parallelupon such opening or on movement of the movable contact away from thestationary contact to produce parallel and reciprocally inductivecurrent fluxes adapted to displace the arc between the arcing horns.

The arcing horns or primary electrodes, according to another feature ofthis invention, consist of metal bars of substantially rectangular crosssection and having throughgoing slots and are mutually divergent in theupward direction as noted earlier; they also are preferably disposed onopposite sides of the arc-quenching chamber so that their divergent legsare inclined upwardly from a common horizontal plane proximal to thecircuit breaker contacts. The inclined legs are disposed symmetricallywith respect to a vertical plane through the chamber which, withreference to the arrangement of the refractory plates and electrodes,may be considered a plane of symmetry.

The chamber itself is provided above the divergent legs of the primaryelectrodes with stacks of refractory and nonconductive plates,preferably of a ceramic such as hard paste porcelain and may define anarcquenching column, the central portion of which is provided with amagnetic circuit adapted to promote the movement of the arc upwardlyuntil the arc is intercepted by the plates which define a zigzag orlabyrinth path for the arc spanning the electrodes, e.g., as describedin the aforementioned copending applications.

The magnetic circuit, according to the present invention, comprises apair of spaced-apart arc displacement horns or secondary electrodeswhich reach down to a horizontal plane just below or coincident with thehorizontal plane of the upper terminus of the inclined legs and arespaced apart by a distance equal to the closest distance between each ofthese secondary electrodes and the closest distance to a proximalprimary electrode. Flanking these secondary electrodes is a pair of polepieces spanned by a magnetic core or are about which the coil means ofthe magnetic circuit may be wound. The secondary electrodes and the polepieces are symmetrically disposed with reference to the aforementionedplane of symmetry and to a further vertical plane of symmetry transverseto this first-mentioned plane. Advantageously, the coil means consistsof a pair of coils connected in series and electrically connected to thesecondary electrodes so as to be energized when the arc jumps to thelatter, thereby producing a magnetic field tending to displace the arcupwardly.

An important feature of this invention resides in the dimensioning ofthe arc-quenching chamber and the positioning of both sets of electrodessuch that an equilateral or regular hexagon is defined between thecontacts and the electrodes and establishes the arc path at a period ofthe order of hundredths of a second (e.g., about 0.01 sec.) afteropening of the movable circuit breaker member.

DESCRIPTION OF THE DRAWING The above and other objects, features andadvantages of the present invention will become more readily apparentfrom the following description, reference being made to the accompanyingdrawing in which:

FIG. 1 is a vertical cross-sectional view through an arcbreaking andquenching arrangement according to the present invention;

FIG. 2 is a detail view illustrating the arrangement of the contacts ofthe system of FIG. 1 and the arc path;

FIG. 3 is a cross section taken generally along the line III III of FIG.1;

FIG. 4 is an enlarged view of the circuit breaking chamber, asillustrated in FIG. I, but with the contacts in the position which theyassume upon incipient opening; and

FIG. 5 is a detail view, in plan, of a portion of an electrode inaccordance with this invention.

SPECIFIC DESCRIPTION The circuit breaker 1 shown in the drawingcomprises the usual mechanism for opening the movable contact of thebreaker arrangement as contained in a housing 1a and not otherwiseillustrated except for an actuating member 1b in the form of a rodextending from this chamber and pivotally connected at 1c to the movablecontact 3.

The circuit breaker also comprises a terminal plate or panel 1d carryingthe insulating posts 1e and 1f forming terminals lg and 1/1 for thehigh-voltage electric current circuit in which the breaker is connected.The panel 1d forms a support for the stationary contact 2 which, asillustrated in FIG. I, is mounted by a bolt 2a upon a conductivepedestal 2b carried by a plate 2c affixed to a copper rod 2d electricalconnection with the terminal 13.

The movable electrode 3 is carried by a lever arm 3a pivotally mountedat 3b upon a support plate 3c affixed to the panel 1d and connected bythe copper rod 3d with a terminal 1h. Upon movement of the rod lbupwardly, the arm 3a is swung in the clockwise sense to bring thecontact face 3e, which is of trapezoidal configuration and composed of alowwear material, such as silver, gold or other noble metal alloy and issubstantially free from pitting, into abutting engagement with thecontact face 2e of the stationary contact 2. Displacement of the rod lbdownwardly swings the lever arm 3a in a counterclockwise sense, e.g.,into the dot-dash position shown in FIG. 1.

Above the circuit breaker assembly 1, whose arc contacts have alreadybeen represented at 2 and 3, I provide an arcquenching chamber 4 whoselower portion 4a is a gas-filled space (in which the gas is air)enclosed between a pair of lateral walls 4b and a pair of transversewalls 40, the walls being assembled by means of bolts 4d as bestrepresented in FIG. 3.

Above the chamber 4a, there are provided two equal quenching columns 5and 6 which will be described in greater detail hereinafter. The primaryelectrodes of the arcquenching system of this invention are constitutedby the arcing horns 7 and 8 mounted by screws 7a and 8a along theinterior of walls 4b and, consequently, at opposite sides of thearc-quenching chamber. The lower ends of the arcing horns 7 and 8 areinclined downwardly and inwardly to constitute legs 7b and 8b whichreach to a horizontal plane H lying just above the arcing contacts 2 and3. The shanks 7c and 8c of the arcing horns 7 and 8 extend verticallyupwardly along the walls 4b and are separated from one another byceramic plates disposed within the sections or columns 5 and 6.

The lower edges of the plates 19 reach to a horizontal plane H disposedabove the plane H and coinciding with the junctions of the legs 7b and8b with the shanks 7c and 8c. The arcquenching chamber 4 and the partsthereof, including the electrodes 7 and 8 are located symmetrically withrespect to the vertical plane Y-Y of FIG. 3 and FIG. 1.

The primary electrode or arc horn 7 has a tab 7d formed with a flange 7ewhich is held in electrical contact with the contact 2 by the screw 2a.Hence the electrode 7 is at the same potential as the contact 2.Similarly the conductive bar 8d is fixed at 8e to an outwardly turnedarm 8fof electrode 8 and is also tied at 83 to the support 30 of arm 30whereby the electrode 8 is at the potential of the contact 3. Thespacing d between the proximal ends of the electrodes 7 and 8 is suchthat the potential at the terminals 1g and 1h is insufiicient to breakdown the gap, absent a transfer of the electric arc thereto from thebreaker contacts.

The sections 5 and 6 are composed of stacks of refractory andnonconductive plates 19 which define zigzag paths represented at Z inFIG. 1 between the primary electrodes 7 and 8 and a pair of secondary orarc displacement electrodes 10 and 11. These plates have, to this end,openings or windows, e.g., as represented in the aforementionedcopending applications.

The secondary or are displacement electrodes 10 and 11 are sheet metalplates as illustrated in FIGS. 1 and 3 and lie along the opposite innerflange of the stacks 5 and 6 whose openings 5 and 6' vent the gases fromthe chamber and define the zigzag arc paths mentioned earlier. Thesesecondary electrodes, also referred to as arc displacement horns l0 and11, have their shanks 10a and 11a lying symmetrically on opposite sidesof the vertical plane of symmetry Y-Y and flanking a magnetic circuitwhich is described in greater detail hereinafter.

A gap b, 11b is maintained between each of these are displacement homs10 and 11 and chambers 12 and 13 which serve the function ofdisplacement arc quenching, the chambers 12 and 13 being provided'withstacks of plates 12a and 13a respectively.

The magnetic circuit comprises a plurality of vertical plates 17 on eachside of the chamber 4 (FIG. 3), connected to a yoke or core 18 ofgenerally rectangular vertical section (FIG. 1) about which coils 14 andare wound in opposite senses but are connected in series (see FIG. 3wherein the series connection of the coils is represented at 15a); thecoils are additionally connected each to a respective arc displacementhorns 10, 11 so as to be energized by the magnetic circuit when the arcreaches these secondary electrodes.

As illustrated in FIG. 4, an essential feature of this invention is theconfiguration of the stationary and movable contacts 2 and 3 in theclosed condition of the breaker and upon incipient opening. To this end,the contact 2 is formed with an upwardly and outwardly turned horn 2fjust above the contact face 2e and reaching toward the lower end of theleg 7b of the primary electrode 7, the surface 2f thereof being roundedso as to facilitate transfer of the are from the contact 2 to the leg7b. Similarly, a horn 3f is provided above the contact face 3e to guidethe arc onto the leg 8b of electrode 8 as the breaker contacts areopened.

More significantly, however, the contacts 2 and 3 are provided below thecontact faces 2e and 3e with confronting generally flat surfaces 21 andrespectively, which lie parallel to one another as shown in FIG. 4 uponincipient opening of the contact 3. As the contact 3 is moved away fromthe contact 2, therefore, the normal current path represented in dotdashlines at 22, 23 and 24 develops the incipient breaking are at 22 At thisinstant, the legs or branches 23 and 24 of the current flux inducesreciprocal magnetic fields which, in accordance with the principles ofinteraction of electric current conductors and magnetic fields, drivesthe are 22 upwardly as represented by the arrow A.

The large section of the two arcing contacts at 20 and 21, permits largecurrent flow through these portions and, consequently, a strong magneticfield to commence the magnetic blast. Consequently, it is important thatthe cross section at C and C of the electrodes 3 and 2, respectively, beconsiderable and larger than the contact zones at 2e and 3e. It is alsocritical to the invention that the distance between the surfaces 20 and21 be as small as possible consistent with the use of contact faces at2e and 3e so that the current arms or branches 23 and 24 will be asclose as possible to one another.

The neck of each of the arcing contacts 2 and 3, below the arc-strikingfaces 2e and 3e should have a rectilinear outline of as large an extentas possible to provide the closed paths for the electric currentbranches 23 and 24 mentioned earlier and provide the strong component ofelectromotive force (arrow A) driving the are 22 upwardly.

Furthermore, the shape and arrangement of the arcing horns or primaryelectrodes 7 and 8 influence the speed and efiectiveness of displacementof the arc and the quenching process. It is, therefore, essential thatthe primary electrodes 7 and 8 be constituted of metal bars havingsubstantially rectangular uniform cross section as well as elongated oroblong slots 9. The slots 9, best shown in FIG. 5, extend through thethickness r of the bars and may have a width at of approximatelyone-third the total width b thereof. The length I of the slots 9 shouldbe at least twice the distance D between the slots and may be up to 10times this distance. Furthermore, the slots 9 should lie centrally ofthe bars 7 and 8. Apparently, the slots 9 facilitate cooling of the barsand promote upward gas flow in the region of the legs 7b and 8b andpossible spreading of the arc to augment the quenching effect. Thecurrent flow may also be branched along the webs between the slots andflanking the same, thereby contributing to the magnetic effect.

Moreover, it has been found that the angle included between the legs 7b,8b and the horizontal will depend upon the voltage which must besustained by the arcing horns or electrodes, for example, it has beenfound that must range between 40 and 50 inclusive for 6 to 12 kv.service and between 30 and 40 inclusive, for 15 to 24 kv. service.

According to an important feature of this invention, the distances x andx of closest approach of the primary electrodes 7 and 8 to the secondaryelectrodes 11 and 10, respectively, and the distance x between thesecondary electrodes 10 and 11 are substantially equal. Furthermore, atabout 0.01 second subsequent to opening of the contacts 2, 3, it isdesirable to insure a spacing x between the faces 2e and 3e and thedistances x and x between the faces 2e and 3e and the lags 7b and 8bwhich are equal to the distances x, x and x so that the arc paths 22,25, 26, etc., define an equilateral hexagon. Consequently, arc portions25 and 26 between the arcing horn 8 and are displacement horn 10 andbetween arcing horn 7 and are displacement horn 11 are equal, and sincesections 5 and 6 of the quenching chamber are of equal dimensions, thequenching plates 19 are equally stressed and more effectivelyexploite'd. Plates 19 are preferably composed of hard past porcelainalthough any refractory material known for this purpose may be used.

The plates forming the auxiliary chambers 12 and 13, however, arecomposed of magnetic metal, according to the present invention and notonly function to break the displacement are but are magneticallyeffective to elongate and split the are by increasing the lengththereof. The hexagonal arrangement mentioned earlier and bestillustrated in FIG. 2, wherein m and n represent the vertices of thehexagon at the lower ends of the arc displacement horns 10 and 11, 0 andr represent the vertices of the hexagon at the ends of the legs 7b and8b of the primary electrode 7 and 8, and p and q represent the contactfaces of the fixed contact and the movable contact, respectively, whenachieved at about l/lOO of a second after opening of the contact,produces maximum upward force to promote the magnetic blast.

Of course, the principles involved here, while described with referenceto a magnetic blast circuit breaker of the airbreak type may be used forgas breakers having dielectrics other than air or for liquid contentbreakers and various mechanisms may be employed for actuating thecontacts. These and other modifications, which will be readily apparentto one of ordinary skill in the art and representing substitution of theequivalents or the like, are intended to be included within the spiritand scope of the appended claims.

I claim:

1. in a circuit breaker, in combination:

a. a pair of breaker contacts connectable in an electric circuit andrelatively displaceable together to close said circuit and apart to opensaid circuit, said contacts having mutually engaging contact facesseparable upon movement of said contacts apart, terminals for connectingsaid contacts in said circuit, and generally flat closely spaced butmutually juxtaposed parallel portions adjacent said faces and betweensaid faces and said terminals for defining parallel electric currentbranches immediately upon opening of said contacts to inducedisplacement of a break arc bridging said faces away from said faces;

b. means defining an arc-quenching chamber above said contacts;

c. arc-splitting electrode means in said chamber in the direction ofdisplacement of said are for subdividing and elongating same, saidelectrode means including a pair of primary electrodes each electricallyconnected with one of said contacts and disposed opposite one anotheracross said chamber, said primary electrodes being formed with metalbars of rectangular cross section and each provided with a multiplicityof spaced oblong throughgoing slots inclined to the horizontaldownwardly and inwardly into the region of said contacts; and a pair ofsecondary are displacement electrodes disposed above said legs and 7. 8spaced from each other and from said legs, said primary and between 40and 50 for a 6 to 12 kv. service circuit. and secondary electrodes beingsymmetrical with respect 3. The combination defined in claim 2 whereinsaid slots exto a vertical plane through said chamber, said primary tendthrough the thickness of said bars and have a width apele ll ng paced rm the r p c v secondary proximately one-third the total width of the barand a length electrodes and Said Secondary electrodes being spacedbetween two and ten times the distance between the slots of apart bysubstantially identical distances to define with h b said contactssubstantially 0.01 second subsequent to the 4 Th bi i d fined in claim 1wherein said P f B of 531d the Vemces of Substamlany chamber is providedwith a stack of refractory nonconductive equilateral hexagon; platesbetween each primary electrode and the associate d. a magnetic circuitin said chamber connected with said secondary electrode Said refractoryplmes defining zigzag Secondary elecuodes mdusmg paths for the arcsbridging said primary and said secondary ment of said are away from saidcontacts, said magnetic electrodes circui including a core between SaidF 5. The combination defined in claim 1 wherein said magelectrodesandacoilelectrtcally connected to said seconneflc circuit comprises apair of pole plates flanking Said deaf-odes for magneuzmg Said core} andchamber and said primary and secondary electrodes. an are a respecnveplate composed of magnenc meta between 5 annin said ole lates betweensaid stacks of refractory each of said secondary electrodes and saidcore while exp g p p tending into Said hexagon to break the displacementare plates, said coil comprises respective series-connected coil and toelongate and split the latter are by increasing the pomons i upon Saldcore and havmg terminals con ength thereof. nected with said secondaryelectrodes.

2 The combination defined in claim 1 wherein said bars 6. Thecombination defined in claim 5 wherein said refracclude with thehorizontal angles ranging between 30 and 40 wry pates we composed ofporcelam' for use of the circuit breaker in a 15 to 24 kv. servicecircuit

1. In a circuit breaker, in combination: a. a pair of breaker contactsconnectable in an electric circuit and relatively displaceable togetherto close said circuit and apart to open said circuit, said contactshaving mutually engaging contact faces separable upon movement of saidcontacts apart, terminals for connecting said contacts in said circuit,and generally flat closely spaced but mutually juxtaposed parallelportions adjacent said faces and between said faces and said terminalsfor defining parallel electric current branches immediately upon openingof said contacts to induce displacement of a break arc bridging saidfaces away from said faces; b. means defining an arc-quenching chamberabove said contacts; c. arc-splitting electrode means in said chamber inthe direction of displacement of said arc for subdividing and elongatingsame, said electrode means including a pair of primary electrodes eachelectrically connected with one of said contacts and disposed oppositeone another across said chamber, said primary electrodes being formedwith metal bars of rectangular cross section and each provided with amultiplicity of spaced oblong throughgoing slots inclined to thehorizontal downwardly and inwardly into the region of said contacts; anda pair of secondary arc displacement electrodes disposed above said legsand spaced from each other and from said legs, said primary andsecondary electrodes being symmetrical with respect to a vertical planethrough said chamber, said primary electrodes being spaced from therespective secondary electrodes and said secondary electrodes beingspaced apart by substantially identical distances to define with saidcontacts substantially 0.01 second subsequent to the spreading of saidcontacts, the vertices of a substantially equilateral hexagon; d. amagnetic circuit in said chamber connected with said secondaryelectrodes for magnetically inducing movement of said arc away from saidcontacts, said magnetic circuit including a magnetic core between saidsecondary electrodes and a coil electrically connected to said secondaryelectrodes for magnetizing said core; and e. a respective plate composedof magnetic metal between each of said secondary electrodes and saidcore while extending into said hexagon to break the displacement arc andto elongate and split the latter arc by increasing the length thereof.2. The combination defined in claim 1 whErein said bars include with thehorizontal angles ranging between 30* and 40* for use of the circuitbreaker in a 15 to 24 kv. service circuit and between 40* and 50* for a6 to 12 kv. service circuit.
 3. The combination defined in claim 2wherein said slots extend through the thickness of said bars and have awidth approximately one-third the total width of the bar and a lengthbetween two and ten times the distance between the slots of each bar. 4.The combination defined in claim 1 wherein said chamber is provided witha stack of refractory nonconductive plates between each primaryelectrode and the associate secondary electrode, said refractory platesdefining zigzag paths for the arcs bridging said primary and saidsecondary electrodes.
 5. The combination defined in claim 1 wherein saidmagnetic circuit comprises a pair of pole plates flanking said chamberand said primary and secondary electrodes, an arc spanning said poleplates between said stacks of refractory plates, said coil comprisesrespective series-connected coil portions wound upon said core andhaving terminals connected with said secondary electrodes.
 6. Thecombination defined in claim 5 wherein said refractory plates arecomposed of porcelain.